3B55.10 Speaker Beats and Interference


Interference and diffraction of sound


A function generator drives two stationary speakers placed in front of the class. The students cover one ear and slowly move their heads around to hear the interference pattern.



  • [1] Function generator
  • [2] Speaker

Classroom Assembly

  1. Turn on the function generator.
  2. Set the amplitude to a minimum.
  3. Set the function generator to produce a 300 Hz sine wave.
  4. Place the two speakers about 2m apart.
  5. Connect a function generator to both speakers.
  6. Slowly increase the amplitude.

Important Notes

  • In large classrooms, the approximate distance the students' head must move to go from high amplitude to low amplitude is longer.


  1. Instruct the students to plug one ear and move their heads from side to side.
  2. Have the students approximate the distance between region of high amplitude and low amplitude.


Additional Resources


  • PIRA 3B55.10


  • Don't attempt this at home!

Last revised

  • 2018


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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.